1. Field of the Invention
The present invention relates to a strand guiding segment for slab casting plants with a guiding width for the cast strand which is adjustable between guide rollers of a frame on a fixed side and a frame on a detachable or loose side, wherein the frames interact with adjusting means for overcoming the ferrostatic pressure and for adjusting the desired sectional width of the strand.
2. Description of the Related Art
The configuration of the strand guiding segments and the base frames is an essential factor for the competitiveness in the field of continuous casting plants. The strand guiding segments and the base frames must meet the operational requirements in an optimum manner, on the one hand, and, on the other hand, they must be competitive with respect to cost, particularly because, depending on the requirements, the portion of the costs of the strand guidance constitutes about 30 to 70% of the total costs of the plant.
Continuous casting plants, particularly continuous casting plants for casting steel slabs, utilize rollers for guiding the strand, wherein the rollers serve to limit the thickness of the strand which is not yet fully solidified and to prevent bulging of the strand shell due to the ferrostatic internal pressure.
For this purpose, groups of at least four pairs of rollers are usually combined into segments. The strand guiding rollers arranged above the strand are mounted on the upper part of the segment or on the detachable frame part, while the strand guiding rollers located below the strand are mounted on the lower part of the segment or the fixed part of the segment. The fixed part and the detachable part of the individual segments are usually connected to each other through four tension cylinders. These so-called clamping cylinders pull the upper part of the segment onto spacers, so that the desired opening width between the oppositely located rollers is obtained. This opening width corresponds to the strand thickness.
Modern process technologies for improving the product quality make it necessary that the opening width can be changed during the casting process. Particularly the so-called soft reduction in the area of the tip of the liquid phase of the strand requires a conical adjustment and a variable opening width adjustment of the corresponding segment. A conventional possibility for changing the opening width of segments with four clamping cylinders is to construct the cylinders with hydraulic servo position control.
DE 196 27 336 C1 discloses a method and an apparatus for guiding a strand in a continuous casting plant with a soft reduction section in which the hydraulic servo units adjust the opening width of the oppositely located strand guiding rollers in an infinitely variable manner. The conventional strand guiding unit, which has in each segment four servo distance/cylinder units for the infinitely variable adjustment of the opening width of the oppositely located strand guiding rollers, is characterized in that the hydraulic lines connect the annular surfaces and piston surfaces of two adjacent servo piston/cylinder units to a common servo valve, and that position pickups of the servo piston/cylinder units controlled by a common servo valve can be coupled to each other through control technology.
The clamping cylinders are usually arranged on the segment laterally next to the rollers and, thus, are located together with the hydraulic lines and servo valves of the servo piston/cylinder units in the range of the radiation influence of the cast strand. Consequently, the clamping cylinders must be arranged at such a distance between the middle of the segment and the hydraulic cylinders that the radiation influence remains within acceptable limits. Because of the load influence on the frames, the required width of the frames of the segment leads to a comparatively great structural weight which, in turn, significantly increases the cost of the manufacture and assembly and the costs of the strands.